Misaligned Bearings Research Articles

Transient characteristics of misaligned roller bearing considering thermal-fluid-solid coupled

Misalignment of roller bearings is a characteristic defect mode, which is accompanied by variations in thermal, mechanical, and lubrication performances. Regarding this aspect, a novel model considering the thermal-fluid-solid coupled effect is proposed to evaluate the performance evolution of lubricated cylindrical roller bearings (CRB) under misalignment states. The proposed model regards structural parameters, contact characteristics, and lubrication status as time-varying variables. By integrating the quasi-static model of CRB with a thermal network model, the influence of internal contact shape and stress on the thermal characteristics of misaligned bearings is reasonably considered. The accuracy of the proposed model is validated through the thermal performance experimental platform. In addition, the influence of thermal and misalignment on time-varying mechanical properties such as contact load, radial stiffness, and clearance loss is assessed. Eventually, the deterioration of the lubrication performance over operational time is quantitatively characterized by the time-varying film thickness at the load region.

Theoretical and experimental investigation on effective length-to-diameter ratio of misaligned water-lubricated bearings

An effective length-to-diameter ratio (ELDR) of the misaligned water-lubricated bearing is investigated in this paper. Firstly, the influence of the length-to-diameter ratio (LDR) on the misaligned bearing is explored theoretically and experimentally. In the theoretical model, liner elastic deformation, local turbulence, and journal misalignment are considered. In the experimental research, the bearing frictional force and hydrodynamic pressure are measured. The results show that an increasing effect of LDR on load-carrying capacity is remarkably weakened for misaligned bearings. On this basis, a concept of effective length-to-diameter ratio is defined. The results show that the bearing part exceeding ELDR has a minor effect on increasing the load-carrying capacity. Thus, the proposed concept of ELDR can be used to evaluate the rationality of bearing length. Finally, the variation law of ELDR with respect to key bearing parameters is analyzed.

Influence of Structural and Operating Parameters on Lubrication Performance of Water-Lubricated Polymer Bearing with Journal Misalignment

Marine water-lubricated polymer bearings support the propeller shaft that stretches out of the ship. The bending deformation of propeller shaft often leads to journal misalignment, significantly impacting the bearing performance. In this paper, a mixed lubrication model for water-lubricated polymer bearing is established considering the effect of journal misalignment, liner elastic deformation, and local turbulence. The influence of key structural and operating parameters on the performance of water-lubricated bearing with journal misalignment is investigated. The results show that the journal misalignment significantly reduces the load-carrying capacity, deteriorates the bearing tribological characteristics, and may cause different axial sections of the bearing to be in different lubrication regimes. Compared with aligned bearings, increasing the length–diameter ratio to improve the load-carrying capacity is significantly weakened for misaligned bearings. Increasing the liner thickness and the load improves axial uniformity of pressure distribution of misaligned bearings. A relatively large clearance ratio decreases the load-carrying capacity and increases the friction coefficient of bearings in the mixed lubrication regime.

Research on the Contact Pressure Calculation Method for the Misaligned Elastomeric Journal Bearing

The pressure distribution of a misaligned elastomeric journal bearing is crucial for analyzing the uneven excessive wearing of the propulsion shaft bearing. However, analysis of the misaligned bearing is usually mainly based on the finite element method (FEM), which lacks a convenient and effective calculation method. This paper uses the influence coefficient factors (ICs) method to analyze the contact pressure of the misaligned bearing. First, the elastic displacement of the cylindrical shell subjected to a single point of concentrated force is derived and used to attain the new influence coefficient factors. Then, the geometric boundary conditions of planar conformal cylindrical contact are extended to the case of non-planar contact. Finally, the proposed method is applied and compared with other methods. The results show that the influence coefficient factors are greatly affected by the shape and constraints of the contact object. The proposed method is suitable for cylindrical shell contact analysis and has the same accuracy as FEM with half of the time consumption. In addition, the bearing capacity and contact stiffness are decreased as the effective contact area decreases due to misalignment.

Mixed-lubrication analysis of misaligned journal bearing considering turbulence and cavitation

By integrating the average flow equation and Ng–Pan turbulence model using the boundary condition of mass conserving [Jakobsson-Floberg-Olsson (JFO)], a mixed lubrication model for misaligned bearing was established considering the effects of turbulence and cavitation. The numerical solution was obtained using a finite difference scheme. The results indicate that the frictional force and moment calculated using the JFO boundary condition are greater than those calculated using the Reynolds boundary condition under the constant external load. In high speed conditions, the turbulence begins to play a role, which makes the maximum oil film pressure and moment decrease and the minimum oil film thickness, cavitation zone, and friction coefficient increase. The boundary condition and turbulence have important effects on the equilibrium position of the axis. The misalignment leads to an obvious increase in the friction of the mixed lubrication area and a slight decrease in that of the hydrodynamic lubrication area.

Effect of ball bearing misalignment on dynamic characteristics of rotor system

A theoretical model with 5 degrees of freedom (DOF) is derived for a rigid rotor system supported by two ball bearings considering the changes of the bearing stiffness due to misalignment. And then radial and axial vibrations of the rotor system and its bearing reactions under different misaligned offsets are investigated with theoretical and numerical analysis. Then, the effects of misalignment on the vibrations of rotor and the bearing, the variation of stiffness and reaction characteristics of the misaligned ball bearing are predicted theoretically. It is concluded that angular misalignment may cause axial vibration and parallel misalignment can bring out extra moment loads for misaligned bearing.

Fatigue Life Analysis of Ball Bearings and a Shaft System Considering the Combined Bearing Preload and Angular Misalignment

Bearing preload significantly affects the running performance of a shaft-bearing system including the fatigue life, wear, and stiffness. Due to the mounting error, the bearing rings are often angularly misaligned. The effects of the combined bearing preload and angular misalignment on the fatigue life of ball bearings and a shaft-bearing system are analyzed in this paper. The contact force distribution of angular contact ball bearings in the shaft-bearing system is investigated based on the system model. The system model includes the bearing model, and the shaft model is verified by comparing with the manufacturer’s manual and the results from other theoretical models, with the difference between the results from the present bearing model and manufacturer manual within 3%. The global optimization method is used to replace the Newton–Raphson algorithm to solve the ball elements’ displacements and friction coefficients, which improves the computation efficiency of the system model. The fatigue life of each bearing is evaluated with the consideration of the two preload methods and two angular misalignment cases. The fatigue life results show that the system life at the optimal angular misalignment is more than 1.5 times that without angular misalignment at the low preload value, and this ratio decreases as the preload value increases. The optimal angular misalignment of both the shaft-bearing system and the misaligned bearing is not always consistent, which depends on the preload value and bearing life. Both the constant-displacement preload and constant-force preload do not cause a significant difference in the highest system life. The different misaligned bearings can lead to different highest system lives as the preload value is low.

Modeling a Hydrodynamic Bearing With Provision for Misalignments and Textures

Abstract Surface texturing is one effective means to improve bearing performance. Available studies are mainly focused on the perfectly aligned journal bearing with textures. The studies involving the effect of surface texturing on the misaligned bearing are still limited. In the present study, a transient mixed lubrication model that allows predicting evolution of friction characteristics with high efficiency was proposed. The misalignment of journal bearing under the time-varying applied load was considered using two deflection angles. The performance of journal bearing with provision for misalignments and textures was studied using the proposed model. The results involving the orbits of the journal center and the energy loss of different misaligned journal bearings were obtained. The influences of misalignment degree and surface texturing on these parameters were analyzed. The results show that along with the increased deflection angles, the effect of texturing on the tribological performance of journal bearing would turn beneficial into harmful.

Internal loads and contact pressure distributions on the main shaft bearing in a modern gearless wind turbine

Abstract The double-row tapered roller bearing (TRB) widely used to support the main shaft in a modern gearless wind turbine is one of the main components and its faults can lead to the malfunctions and downtime of wind turbines. Over the past decades, some numerical approaches have been proposed for calculating the contact force and pressure distribution of double-row TRBs. Nevertheless, most of the existing studies did not take the angular misalignment between inner and outer rings and the frictional force between the rollers and raceways into account. This paper presents a comprehensive quasi-static model to investigate the internal load and contact pressure distribution in a double-row TRB by considering the angular misalignment, the combined external loads and frictional force. It is found that a small misalignment angle between inner and outer rings can result in a significant change in the magnitude and distribution of the contact force and pressure. The double-row TRB with crowned roller profile exhibits a substantial improvement in contact pressure distribution by eliminating the occurrence of pressure concentration. Moreover, the peak contact pressure can be significantly reduced on the roller with the crowned profile, even if in the case of misaligned bearing. Comparisons of the simulated contact loads and pressure distributions demonstrate the necessity of considering angular misalignment and frictional force in the modelling of large size and heavily loaded double-row TRB.

Influence of micro-grooves on the lubrication performance of a misaligned bearing

Surface texturing for improving the lubrication performance of journal bearings has been widely investigated in the last two decades. In practical applications, the misalignment of a journal bearing occurs due to the asymmetric bearing load, elastic deflection, manufacturing tolerances, and installation errors. However, there has been little discussion on the influence of grooves on the lubrication performance of misaligned bearings. In the present work, numerical predictions of lubrication performances are presented to test the influence of the grooves. Based on the JFO boundary condition, a mass conservation algorithm is implemented to automatically determine the position of oil film rupture and reformation. The load-carrying capacity, friction force, friction coefficient, and bearing moment are computed numerically. The influence of angular position of the groove is first conducted in a misaligned bearing. Subsequently, the groove depth and width are investigated with different values of [Formula: see text] and [Formula: see text] ratios, respectively.

Thermoelastohydrodynamic analysis of misaligned bearings with texture on journal surface under high-speed and heavy-load conditions

Hydrodynamic journal bearings are used to support the planetary gears in the transmission system of a Geared Turbo Fan engine, and they operate under severe working conditions, such as misalignment, high speed, and heavy load. Surface texture is regarded as an effective approach to improve mechanical properties under severe working conditions. However, the effects of surface texture on misaligned journal bearings under severe conditions have not been well studied. Therefore, a thermoelastohydrodynamic (TEHD) lubricating model with a textured and misaligned journal is presented in this study. Solid deformation, heat transfer between oil and the bearing, and heat convection between air and the bearing are considered in the model. The effects of cavitation and viscosity-temperature are also taken into account. The impacts of surface texture parameters and the misalignment angle on lubricating properties are investigated in the model. Results indicate that the bearing lubricating performance is greatly improved by optimal surface texture considering journal misalignment. The maximum oil film pressure and load-carrying capacity of a journal bearing increase with journal misalignment. Meanwhile, the oil film temperature increases sharply while considering misalignment.

Mixed-lubrication analysis of misaligned bearing considering turbulence

Abstract Some bearings operate in mixed-lubrication regime due to the low rotational speed and the heavy load and misalign due to shaft's gravity. For large bearings, the maximum film thickness is much larger than minimum nominal film thickness and turbulence may locally develop. This paper proposes an approach to analyze misaligned mixed-lubrication bearing considering turbulence. Based on the average flow model proposed by Patir and Cheng and the Ng-Pan turbulence model, a generalized average Reynolds equation is derived. The calculation procedure is established by finite difference method. The results show that turbulence remarkably increases friction coefficient, slightly increases the minimum nominal film thickness, and decreases the transition speed from mixed-lubrication regime to hydrodynamic lubrication regime.

On the performance of foil thrust bearing with misaligned bearing runner

PurposeCompliant foil thrust bearings are promising bearings for high-speed oil-free turbomachinery. However, most previous experimental and numerical approaches to investigate the performance of these bearings have ignored the effect of bearing runner misalignment. Therefore, this paper aims to evaluate the effects of static and dynamic angular misalignments of the bearing runner on the performance of a gas-lubricated foil thrust bearing.Design/methodology/approachThe bearing runner is allowed a maximum angular misalignment that produces a minimum gas film thickness as low as 20 per cent of the nominal clearance. Then, the variations of bearing load carrying capacity, viscous power loss and stiffness and damping coefficients of the gas film with runner misalignment are thoroughly analyzed. The flow in the gas film is modeled with compressible Reynolds equation along with the Couette approximation technique, and the deformation of the compliant bearing is calculated with a robust analytical model. Small perturbations method is used to calculate the force and moment dynamic coefficients of the gas film.FindingsThe results show that misaligned foil thrust bearings are capable of developing a restoring moment sufficient enough to withstand the imposed misalignments. Furthermore, the enhanced hydrodynamic effect ensures a stable operation of the misaligned bearing, and the results highlighted the role of the compliant bearing structure to maintain foil bearing prominent features even at misaligned conditions.Originality/valueThe value of this study is the evaluation of the effects of runner angular misalignments on the static and dynamic characteristics of Generation II bump-type foil thrust bearing.

Analysis of misaligned journal bearing with herringbone grooves: consideration of anisotropic slips

The effects of anisotropic slip on the lubrication performance of misaligned journal bearings with herringbone grooves are discussed in this study. The modified Reynolds equation, which considered the anisotropic slips, and film thickness equation in misaligned bearings are solved numerically by the finite element method (FEM). The effects of misaligned angle and anisotropic slip on the load capacities and friction force of journal bearings are analyzed. The results show that the existence of slip boundary conditions can dilute the effects of misalignment for journal bearings. Finally, the effects of moment position and dimensionless pressure on the bearing are also discussed.

Analysis of thermoelastohydrodynamic performance of journal misaligned engine main bearings

To understand the engine main bearings’ working condition is important in order to improve the performance of engine. However, thermal effects and thermal effect deformations of engine main bearings are rarely considered simultaneously in most studies. A typical finite element model is selected and the effect of thermoelastohydrodynamic(TEHD) reaction on engine main bearings is investigated. The calculated method of main bearing’s thermal hydrodynamic reaction and journal misalignment effect is finite difference method, and its deformation reaction is calculated by using finite element method. The oil film pressure is solved numerically with Reynolds boundary conditions when various bearing characteristics are calculated. The whole model considers a temperature-pressure-viscosity relationship for the lubricant, surface roughness effect, and also an angular misalignment between the journal and the bearing. Numerical simulations of operation of a typical I6 diesel engine main bearing is conducted and importance of several contributing factors in mixed lubrication is discussed. The performance characteristics of journal misaligned main bearings under elastohydrodynamic(EHD) and TEHD loads of an I6 diesel engine are received, and then the journal center orbit movement, minimum oil film thickness and maximum oil film pressure of main bearings are estimated over a wide range of engine operation. The model is verified through the comparison with other present models. The TEHD performance of engine main bearings with various effects under the influences of journal misalignment is revealed, this is helpful to understand EHD and TEHD effect of misaligned engine main bearings.

Study on thermoelastohydrodynamic performance of bearing with surface roughness considering shaft deformation under load in shaft‐bearing system

PurposeCurrent lubrication analyses of misaligned journal bearings are generally performed under some given preconditions. The purpose of this paper is to calculate the lubrication characteristics of a journal bearing with journal misalignment caused by shaft deformation under load, considering the surface roughness, thermal effect and (thermal and elastic) deformation of bearing surface simultaneously.Design/methodology/approachThe lubrication of bearing was analyzed by average flow model based generalized Reynolds equation. The deformation of bearing surface under pressure or heat of oil film was calculated by compliance matrix method. The compliance matrix was established by finite element analysis. The temperature distributions of oil film and bearing were calculated by energy equation and heat conduction equation.FindingsWhen the thermal deformation of bearing and journal surface is considered, the radius clearance affects not only the value of the maximum oil film pressure and minimum oil film thickness, but also the distribution of oil film pressure and thickness of misaligned bearing. The effect of thermal deformation of bearing on the performance of misaligned bearing is larger than that of elastic deformation of bearing. Whether or not the surface roughness affects the performance of misaligned bearing and the affecting level depends greatly on the condition of deformation of bearing surface.Originality/valueThe surface roughness, thermal effect and (thermal and elastic) deformation of bearing surface were considered simultaneously in the thermoelastohydrodynamic lubrication analysis of bearing with journal misalignment caused by shaft deformation under load. The results of this paper are helpful to the design of the bearing.

A Hybrid Mobility Solution Approach for Dynamically Loaded Misaligned Journal Bearings

This paper presents a hybrid mobility solution approach to the analysis of dynamically loaded misaligned journal bearings. Mobility data obtained for misaligned bearings (calculated from a finite element representation of the Reynolds equation) are compared with existing curve-fitted mobility maps representative of a perfectly aligned bearing. A relative error analysis of mobility magnitude and direction provides a set of misaligned journal bearing configurations (midplane eccentricity ratio and normalized misalignment angle), where existing curve-fitted mobility map components based on aligned bearings can be used to calculate the resulting journal motion. For bearing configurations where these mobility maps are not applicable, the numerical simulation process proceeds using a complete finite element solution of the Reynolds equation. A numerical example representing a misaligned main bearing in a four-stroke automotive engine illustrates the hybrid solution method. Substantial savings in computational time are obtained using the hybrid approach over the complete finite element solution method without loss of computational accuracy.

A Study of Misaligned Micropolar Lubricated Membrane Compensated Hybrid Journal Bearing System

The present work aims to analytically study the performance of misaligned four-pocket, membrane compensated, hybrid journal bearing system operating with micropolar lubricant. In the present study, the flow characteristic of the lubricating oil containing additives and contaminants has been modeled using Erigen’s micropolar theory. The journal misalignment which may occur as a result of noncentral loading, improper assembly, shaft deflection due to elasticity and thermal distortions, etc. has been accounted for in the present study by defining a pair of misalignment parameters in vertical and horizontal directions (i.e., δ and σ).The modified Reynolds equation governing the flow of micropolar lubricant in the clearance space of a misaligned bearing has been solved using FEM and Newton Raphson method along with the appropriate boundary conditions. The numerically simulated results suggest that the effect of journal misalignment is to cause degradation in bearing performance, whereas the influence of micropolar effect of lubricant is to enhance the bearing performance. Therefore, it is imperative to account for the effect of misalignment and lubricant behavior during the design process in order to generate accurate bearing characteristics data.

Thermohydrodynamic Lubrication Analysis of Misaligned Plain Journal Bearing With Rough Surface

Journal misalignment exists generally in journal bearings. When severe journal misalignment takes place, the minimum film thickness of journal bearings reduces greatly. In this condition, the surface roughness, the oil viscosity-pressure relationship (VPR), and the thermal effect have obvious effects on hydrodynamic lubrication performance of misaligned bearings. In this paper, the oil film pressure, oil film temperature, load-carrying capacity, end leakage flow rate, frictional coefficient, and misalignment moment of a journal bearing with different angles of journal misalignment and surface roughness, and considering oil VPR and thermal effect, were calculated based on the generalized Reynolds equation, energy equation, and solid heat conduction equation. The results show that the oil VPR and surface roughness have a significant effect on the lubrication of misaligned journal bearings under large eccentricity ratio. The thermal effect will affect obviously the lubrication of misaligned journal bearings when eccentricity ratio and angle of journal misalignment are all large. In the present design, the size of the journal bearing is compact more and more, and the eccentricity ratio and angle of journal misalignment are usually large in operating conditions. Therefore, it is necessary to take the effects of journal misalignment, surface roughness, oil VPR, and thermal effect into account in the design and analyses of journal bearings.

Research on elastohydrodynamic lubrication of a crankshaft bearing with a rough surface considering crankshaft deformation

Journal misalignment in bearings caused by crankshaft deformation under load exists generally in internal combustion engines. When serious journal misalignment takes place, the minimum oil-film thickness of bearings is greatly reduced and the maximum oil-film pressure of the bearings increases markedly. Therefore, it is necessary to consider the surface roughness and deformation of bearing surface when analysing the hydrodynamic lubrication characteristics of a misaligned bearing. In this paper, the elastohydrodynamic lubrication properties of crankshaft bearings considering crankshaft deformation under load and the surface roughness for a four-cylinder internal combustion engine were studied. The lubrications of the crankshaft bearings were analysed by the dynamic method. The deformation of the bush surface under the oil-film pressure was calculated by the deformation matrix method. The results show that, when crankshaft deformation is considered, the surface roughness has a marked effect on the orbits of the crankshaft bearings, but deformation of the bearing surface scarcely affects the orbits of the crankshaft bearings. When the surface roughness of a bearing is considered, the maximum oil-film pressure of crankshaft bearings obviously increases, the minimum oil-film thickness decreases markedly, and the end flowrate changes little in most of the engine cycle. When elastic deformation of the bearing surface is considered, the maximum oil-film pressure of bearings decreases to a different extent: elastic deformation of the bearing surface affects the end flowrate, the frictional coefficient of the journal, and the minimum oil-film thickness very little.